The inventive concept relates to a method of manufacturing a semiconductor, and to a method of manufacturing a photomask used in photolithography.
A plurality of circuit patterns (or photoresist patterns) are formed on a wafer by using a photolithography process. In particular, as the design rule of a semiconductor device decreases, the importance of critical dimension (CD) uniformity of semiconductor patterns increases.
The CD uniformity of semiconductor patterns is affected by optical elements such as a light source, a lens, and an aperture. Highly-integrated devices are affected by CD uniformity of photomask patterns. The CD uniformity of mask patterns must increase so as to increase the CD uniformity of circuit patterns formed on the wafer.
The CDs of mask patterns may be measured and corrected using a scanning electron microscope (SEM) method or an optical critical dimension (OCD) method. In the SEM method, the CDs of a large number of photomask patterns are directly measured using electron beams so as to adjust the global uniformity of photomasks by accounting for measurement errors of equipment and local CD errors of the photomasks. However, in a current mass production process, only local CDs of photomask patterns are measured so as to increase production efficiency. Thus, the global uniformity of photomasks cannot be accurately corrected using the SEM method.
In the OCD method, after photoresist patterns are formed on a wafer using a photolithography process, CDs of photomasks are determined by measuring the reflection index (or reflection spectrum) of the photoresist patterns, and the measured CDs are corrected. In order to correct the CDs of mask patterns in the OCD method, parameters such as CDs of photoresist patterns, CD change amount due to the exposure energy (intensity of exposure source) during the photolithography process, and a CD correction amount according to an exposure condition must be measured. In this case, in order to measure and correct the CDs of photomasks using the OCD method, the photolithography process must include an exposure process, and the correction parameters must be measured. Thus, process time increases, which lead to an increase in the cost of the manufacturing process. Thus, a method for obtaining the correct global uniformity of photomasks without performing the photolithography process is required.
In addition, when using the OCD method, the measurement equipment for measuring a reflection index can be used to measure only the resultant shape of a diffraction pattern and thus cannot be used to measure a variety of patterns that are commonly used.